Low-Cost Micro-Assembly Machine
V Koichi Shimamura
V Yasunori Sasaki
V Masanao Fujii
(Manuscript received May 31, 2006)
Recently, production demand in manufacturing industries has changed drastically from
demand for high-mix, low-volume production to that for high-mix, variable-volume
production. At Fujitsu, we are promoting innovative engineering through the effective
use of existing equipment without the need for additional investments and by implementing the Toyota Production System. Two major themes of manufacturing in the
future will be the creation of strong production systems that can adapt to market changes while holding down investment and eliminating waste and the development of equipment suitable for those changes. To assist in this area, Fujitsu now offers a low-cost,
ergonomically designed micro-assembly machine that can be used in comprehensive
applications ranging from small trials to mass-production. This machine has the high
speed and accuracy of existing equipment and provides greater flexibility and
economy during manufacturing and product changes. This paper describes this new
machine.
1. Introduction
Recent years have seen a drastic change in
the production demand in manufacturing industries from demand for high-mix, low-volume
production to that for high-mix, variable-volume
production1),2) and the increasing implementation
of production systems such as the Toyota Production System and the cell production system.3) For
example, in the electronic device field that
supports the production of information transmission equipment, rapid progress can be seen in
product downsizing and sophistication even while
product lifecycles have become extremely short.
The equipment required for the production of
these ultra-small devices, from small trials
through to mass-production, must be physically
small while at the same time enable the use of
high-precision processing and mounting technologies and flexible, precise, low-vibration handling
technology. Frequent changes to the component
elements and processes occur at the small trial
FUJITSU Sci. Tech. J., 43,1,p.59-66(January 2007)
level, and therefore the mounting and assembly
equipment must be able to handle such changes
with speed and flexibility. At the mass-production level, high throughput and expandability are
being demanded. Furthermore, compact, low-cost
equipment is required at both the trial production and mass-production levels. At Fujitsu, we
are currently developing a low-cost micro-assembly machine that enables the construction of a
desktop production line.
In this paper, we describe the development
of the high-precision positioning technology
employed in our low-cost micro-mounting and
assembly unit. We then describe the development
of our parts supply technology, which is one of the
most important technologies for the effective use
of the unit and the production line. Finally, we
describe the low-cost micro-assembly machine
that was designed with these development
technologies at its base.
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K. Shimamura et al.: Low-Cost Micro-Assembly Machine
2. Development of automated
equipment for high-mix,
variable-volume production
In this section, we first describe the automatic assembly machine we designed for high-mix,
variable-volume production.
2.1 Issues concerning production diversity
At Fujitsu, it was general practice to use a
die bonder,note) which is a machine that enables
high-speed, high-precision mounting and assembly of micro-devices. A die bonder is ideal for
high-volume production, but is not suited to
high-mix, variable-volume production such as that
required at the trial production level. This is
because of the machine’s high initial investment
cost, long period before stable operation, and large
size.
Moreover, the component elements used to
configure this equipment are becoming increasingly modular and downsized, and space-saving,
energy-efficient desktop robots are also being
offered to enable setup in a short time frame.
However, in fields where the mounting and
assembly of sensor devices and so forth have a
direct influence on product performance, it is
difficult to say that the high-speed, high-precision
handling requirements are being met by this type
of equipment. The following is an overview of the
mounting and assembly equipment required for
this type of high-mix, variable-volume production.
1) In general, trial products are manufactured
several times in a company’s product development
department in the pre-mass-production stages.
Most of the pieces of equipment used to manufacture these trial products are combinations of
simple general-purpose units that are mainly
manually operated, and the manufacturing
conditions and other important details are
note)
60
A machine with a surface area of approximately 1 square meter, a height of around
1.5 meters, and a weight of several 100 kgf
used to mount chips cut out of wafers onto
lead frames and ceramic substrates at high
speed and with a high level of precision.
determined by the simplicity of the equipment
used. For mass-production, the manufacturing
conditions must be further adjusted to match those
of high-precision manufacturing equipment,
thereby requiring a considerable amount of time
to establish mass-production operation. Accordingly, there is a demand for assembly equipment
that can be used for both trial production and
mass-production without having to change the
setup in between.
2) Current demands with regard to high-mix,
variable-volume production are for the ability to
handle short-term, high-volume production and
for equipment that can flexibly handle model
changes while still maintaining high-speed
production.
3) A compact, low-cost assembly machine that
delivers high space productivity and can also be
used for several product generations will become
necessary.
2.2 Development policy and product
concept
To provide solutions to the issues described
above, as the central theme of our development
policy, we started development of a fast, automated, and compact assembly machine that uses a
base machine concept. We then developed a lowcost micro-assembly machine.
1) Compact design
Our aim was to develop an automatic assembly machine with the frame, mechanisms, and
controls all contained in a single 100 mm-width ×
300 mm-depth × 300 mm-height unit that weighed
less than 10 kgf so it could be carried by one
person. The assembly machine would enable
standalone desktop operation and be linkable with
other assembly machines to form an instant
production line. This product concept enables a
fast, flexible response to changes in the production process. Moreover, making the unit assembly
machine compact and lightweight increases its
rigidity, and because it is not affected by the
installation conditions, it delivers high speed and
FUJITSU Sci. Tech. J., 43,1,(January 2007)
K. Shimamura et al.: Low-Cost Micro-Assembly Machine
3. Micro high-precision
positioning technology
To combine high-precision mounting and assembly operations with high-order assembly line
functions within a restricted space, we developed
a conveyance/positioning mechanism with a builtin feed function, as well as a visual recognition
alignment technology.
1) Conveyance/positioning mechanism technology
The positioning error of the mechanism due
to the dimensional tolerances and thermal expansion/contraction of its mechanical components can
be reduced by limiting the mechanism’s operational range. Therefore, the high-precision parts of
this mechanism use ball screws with small travel
ranges and roller conveyers are only used in the
conveyance mechanism. The ball screws and
roller conveyers are contained in the same
mechanism but are independent of each other, and
the use of roller conveyers simplifies the conveyance mechanism. The repeat positioning precision
is shown in Figure 1. This is a good example of a
FUJITSU Sci. Tech. J., 43,1,(January 2007)
high-precision ball-screw mechanism, and we can
see that the precision is improved by restricting
the drive area to the fixed-end side of the drive
mechanism unit.
2) Image-processing alignment technology
using visual recognition
Mounting and assembly requires not only a
high repeat positioning precision in the handling
mechanism, but also highly precise alignment of
the workpiece and the part to be mounted. In particular, when parts become smaller and a datum
plane cannot be established, measurement/correction of the parts’ shapes and any positional or
rotational shift at the parts’ mounting positions
is required for optimum positioning. When
developing this technology, we used a workpiece
recognition system combined with a parts recognition system to minimize the effects of stack
measurement errors from the mechanism’s components and position shifts due to temperature
fluctuations. As a result, we were able to establish a stable, high-speed, and high-precision
positioning technology that is not affected by the
shapes of the workpiece and parts or by the
condition of their surfaces. The recognition
Fixed end
Motor
Stage
Free end
6
4
Repeatability (µm)
high precision.
2) Base machine concept
The assembly machine comprises a base
machine consisting of the frame and a conveyance/
positioning mechanism and a custom unit with
hand unit and automatic alignment mechanisms
that directly access the workpieces and assembly
parts. The use of a base machine reduces costs
and development time and enables the assembly
machine to be used over several product generations. Moreover, because the custom unit is
independent of the base machine, technological
resources can be concentrated on the development
of elemental technologies, leading to an improvement in the quality of the assembly machine.
In the following sections, we introduce the
micro high-precision positioning technology and
the parts supply technology that are the principal technologies of the low-cost micro-assembly
machine. We then describe the low-cost microassembly machine itself.
2
0
0
10
20
30
40
50
-2
-4
-6
Position from fixed end (mm)
Figure 1
Relationship between distance and positioning precision.
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K. Shimamura et al.: Low-Cost Micro-Assembly Machine
repeatability (precision and time required when
the number of edge scan lines has been selected
as the parameter) for the central positions when
edge measurements have been applied to the
stepped section of a metal motor hub is shown in
Figure 2.
4. Parts supply technology
To enable a certain degree of unattended
operation, conventional mass-production equipment uses a system that automatically supplies
parts from a large stock of parts contained inside
the equipment. However, manufacturing this kind
of system is a major, high-cost undertaking, and
it is difficult to change it so it can handle a different product or use it for other applications.
Moreover, this type of system does not meet the
requirements for innovative manufacturing
balanced with operational efficiency, where the
stock quantity is maintained at as small a level
as possible to eliminate product stagnation. On
the other hand, to downsize products, parts are
becoming increasingly micro-sized, making them
difficult for humans to handle. Simple, automated supply units are therefore being demanded.
Against this background, we developed a lowcost micro-parts supply unit for use with the
300
6
X direction (3 σ)
Y direction (3 σ)
5
250
4
200
3
150
2
100
1
50
0
0
50
100
150
200
250
Number of scan lines
Figure 2
Recognition precision.
62
300
0
350
Time required (ms)
Precision XY (µm)
Time required
assembly machine that we developed.
1) Parts supply technology employing a tray
The parts supply unit that we developed
targets the widely-used 2-inch and 4-inch trays,
because these are the most suitable trays for the
parts sizes and stock quantities in general use.
The parts are laid out on the tray in a
matrix, and the mechanism we developed feeds
the tray to suit the arrangement of the parts so
they can be picked up. Because the Y-direction
uses the Y-axis of the hand, this unit only has an
X-axis, which is also the X-axis of the workpiece.
The unit is only 100 mm × 100 mm × 8 mm, so it
can easily be mounted in the assembly machine.
The X-axis stroke is designed to be around 50 mm
for the 2-inch size trays. For the 4-inch trays, the
mechanism repositions the tray at the location
where the full axis stroke has been reached.
2) Micro-sized parts supply technology
The conventional system generally used by
a parts supply unit to retrieve micro-sized parts
one by one from an aggregation of diverse parts is
a vibratory bowl feeder that aligns the parts
around its perimeter for retrieval. Depending on
the size of the bowl feeder, a large quantity of parts
can be dumped into it, and various shapes can be
handled by using a sorting mechanism during the
alignment process. However, because a customized bowl of a particular shape and design to suit
the parts being fed is required, difficulties arise
when it is necessary to handle different kinds of
parts, and the costs are comparatively high.
We therefore developed a unit that can
supply parts using only compressed air. As shown
in Figure 3, compressed air is fed to the parts in
the bowl, and the parts are carried along as the
air flows towards the bowl’s outlet (the parts
supply opening). By controlling the airflow in the
bowl, parts having various shapes, for example,
micro-sized balls with a diameter of 0.1 to
0.2 mm, 0603 chips with a size of 0.6 × 0.3 mm,
and micro screws with a size of M1.2 or smaller,
can be handled. We were able to develop a lowcost supply unit capable of supplying 1000 to 3000
FUJITSU Sci. Tech. J., 43,1,(January 2007)
K. Shimamura et al.: Low-Cost Micro-Assembly Machine
Airflow
Part supply opening
Y-axis unit
Z-axis hand
Assembly pallet Control device
Aligner
300 mm
Control
device
100 mm
Precision stage Frame
Compressed air exhaust port
Figure 3
Principle of bulk supply.
parts at a time.
5. Low-cost micro-assembly
machine
In this section we describe the low-cost micro-assembly machine that we developed using the
technologies described earlier in this paper.
1) Low-cost micro-assembly machine
As shown in Figure 4, this assembly
machine comprises the following three elements.
•
A frame with a built-in unit that is used for
both multiple parts mounting and assembly
processes and a common base comprising the
conveyance/positioning mechanism described
in Section 3.
•
A precision stage selection base equipped
with Y-axis and alignment mechanisms for
selecting the operating stroke and loadbearing capacity according to the process
conditions.
•
A custom aligner/Z-axis hand unit.
The basic configuration is pick-and-place.
The basic operation flow is as follows. A part
that has been positioned by the aligner is held by
the hand, moved to and positioned by the Z-axis
and Y-axis pick-and-place operations over the
workpiece mounted on the assembly pallet, and
then mounted on the workpiece. After the part
FUJITSU Sci. Tech. J., 43,1,(January 2007)
Conveyance/
positioning
mechanism
300 mm
Control device
Figure 4
Configuration of low-cost micro-assembly machine.
has been mounted, the assembly pallet is fed out
using the feed function of the conveyance/positioning mechanism. A positioning repeatability
precision of 3 µm has been realized, which makes
this unit suitable for mounting sensor devices.
2) Line operation
As shown in Figure 5, an assembly line can
be created simply by placing multiple assembly
machines next to each other to form a line. That
is, the linking of several of the conveyance/
positioning mechanisms described earlier enables
them to function as a conveyor unit, thereby
creating a compact mounting and assembly line
on the desktop. Moreover, the movable frame
features a slide-out function to improve servicing
of the machines mounted on the frame and to
enable manufacturing process changes to be performed easily. When mounting chips in a package,
if the assembly machines for the adhesive application process, chip mounting process, and
adhesive hardening process are developed to
accommodate the conditions required for each
process and then linked together in a line, an
automated line can be constructed that can
handle production runs from the trial production
level through to mass-production.
3) Assembly machine with built-in visual recognition functions
An assembly machine with built-in visual
recognition functions is shown in Figure 6. This
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K. Shimamura et al.: Low-Cost Micro-Assembly Machine
Workpiece recognition camera
Hand
Workpiece
Pick-and-place
robot
Movable frame
(Conveyance/positioning mechanism)×N
Conveyor
Figure 5
Assembly line.
machine consists of a conveyance/positioning
mechanism, pick-and-place robot and hand, parts
recognition camera, and workpiece recognition
camera. The basic operation is as follows. The
pick-and-place robot picks up a part and mounts
it on the workpiece after any misalignment of the
workpiece on the conveyance/positioning mechanism has been recognized and corrected. For a
product in which a magnetic hard disk medium
was mounted onto a motor hub, we achieved a
visual recognition repeatability of within 1 µm.
4) Assembly machine with a parts supply unit
The precision stage and the aligner units of
the assembly machine shown in Figure 4 can be
replaced with different types of parts supply units.
For example, as shown in Figure 7, the precision
stage and aligner can be replaced by a parts supply unit that uses a motor to perform positioning
control of the tray. Moreover, if a bulk supply unit
is mounted instead of the aligner on the stage,
the parts supply opening can be automatically
adjusted for the type of parts being supplied.
Figure 8 shows an assembly machine for the
supply and mounting of balls with a diameter of
0.1 to 0.2 mm. Apart from spherical parts, this
machine can also be used to supply rectangular
parallelepiped parts such as 0603 chips or screws.
Moreover, because a supply unit can be constructed with a width of only 10 mm, multiple supply
units can be incorporated in a single assembly
unit. Accordingly, a single assembly machine can
be used to mount multiple parts.
64
Conveyance/positioning
mechanism
Part
Provisional positioning stand
Part recognition camera
Figure 6
Image-processing assembly machine.
4-inch tray
Tray positioning mechanism unit
Figure 7
Part supply unit employing a tray.
5)
Results
Using the conveyance/positioning mechanism technology and the visual recognition
position alignment technology that we developed,
we realized an easily transportable low-cost
micro-assembly machine with high-speed and
high-precision characteristics and a base machine
structure. This machine has enabled the construcFUJITSU Sci. Tech. J., 43,1,(January 2007)
K. Shimamura et al.: Low-Cost Micro-Assembly Machine
Y-axis hand
Mounted
head
Bulk supply unit
Conveyance/positioning
mechanism
Figure 8
Bulk supply unit and assembly machine.
tion of an automated system with the flexibility
to speedily adapt to the manufacturing process
and product changes that will become necessary
as parts become more diversified in shape and
further progress is made in the development of
the technology used to manufacture low-cost
supply units for micro parts. The micro-assembly
machine that we developed is already
being used to create systems that can be used
consistently from trial production through to
mass-production.
6. Conclusion
As we pointed out at the start of this paper,
production demand in manufacturing industries
has changed drastically from demand for
high-mix, low-volume production to that for
high-mix, variable-volume production. At Fujitsu,
two major themes of manufacturing in the future
will be the creation of production systems that can
adapt to market changes while holding down investment and eliminating waste and the
development of equipment suitable for those
FUJITSU Sci. Tech. J., 43,1,(January 2007)
changes.
Several demands are being made of the
equipment that will enable innovative manufacturing line changes: incorporation of the
one-unit-flow concept, a speedy and flexible
response to changes in the manufacturing process,
compact size and economy, compatibility with the
human-based operations performed in the cell
production method, and high-speed and highprecision characteristics that are inherent in the
equipment itself. Moreover, to reduce the manufacturing preparation time and strengthen
innovative development to improve the design and
development quality, further developments such
as equipment platformization, equipment units
that can be used for multiple product generations,
and the concentration of development resources
on leading-edge manufacturing technology will be
required. The low-cost micro-assembly machine
and the parts supply unit described in this paper
are examples of effective measures that meet these
demands. In the future, the Fujitsu Group as a
whole will endeavor to play a key role in the
strengthening of innovative manufacturing and
development policies.
References
1)
2)
3)
T. Arai: Learn from a Highly-Reputed Automatic
Assembly Line. (in Japanese), The Japan
Society for Precision Engineering, Technical Committee for Production Automation publication,
Issue 91, 2004, p.1-4.
Japan Robot Association: Using Robots to Open
Business Frontiers. (in Japanese), Japan Robot
Association, Robot Policy Society publication,
2005, p.11-12.
Special Issue 1: The Unknown CANON. (in Japanese), Diamond Weekly, 93, 3, p.36-39 (2005).
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K. Shimamura et al.: Low-Cost Micro-Assembly Machine
Koichi Shimamura, Fujitsu Ltd.
Mr. Shimamura received the B.S. degree
in Mechanical Engineering from Yamanashi University, Yamanashi, Japan in
1982. He joined Fujitsu Ltd., Kanagawa, Japan in 1982, where he has been
engaged in research and development
of automatic assembly systems. He is
a member of the Japan Robot
Association.
Masanao Fujii, Fujitsu Ltd.
Mr. Fujii received the B.E. and M.E.
degrees in Production Mechanical Engineering from Tottori University, Tottori,
Japan in 1988 and 1990, respectively.
He joined Fujitsu Ltd., Kanagawa,
Japan in 1990, where he has been
engaged in research and development
of interconnect technology for printed
circuit boards. Since 1999, he has also
been engaged in research and
development of assembly technology and machines for
micro-devices.
Yasunori Sasaki, Fujitsu Ltd.
Mr. Sasaki received the B.S. degree in
Mechanical Engineering from Shinshu
University, Nagano, Japan in 1984. He
joined Fujitsu Ltd., Nagano, Japan in
1984, where he was engaged in SMT
and BMT manufacturing engineering.
He was assigned twice to a North American manufacturing site. He is now at
Fujitsu Ltd., Kanagawa, Japan, where
he is engaged in development of micro
device assembly technology.
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FUJITSU Sci. Tech. J., 43,1,(January 2007)